JLG 120HX ANSI Service Manual - Manual (Page 53)

SECTION 2 - PROCEDURES
3120686 – JLG Lift – 2-33
Wear Tolerance
1. From the underside of the machine, at rear center,
with the boom fully elevated and fully retracted (See
Figure 2-16.), using a magnetic base dial indicator,
measure and record the distance between the swing
bearing and the frame. (See Figure 2-17.)
2. At the same point, with the boom at horizontal
extended until red marking band on mid section is
exposed (See Figure 2-16.), using a magnetic base
dial indicator, measure and record the distance
between the swing bearing and frame. (See Figure
2-17.)
3. If a difference greater than 0.064 in. (1.625 mm) is
determined, the swing bearing should be replaced.
4. If a difference less than 0.064 in. (1.625 mm) is
determined, and any of the following conditions
exist, the bearing should be removed, disassem-
bled, and inspected for the following:
Metal particles in the grease.
Increased drive power required.
Noise.
Rough rotation.
5. If bearing inspection shows no defects, reassemble
bearing and return to service.
THE SWING BEARING IS ONE OF THE MOST CRITICAL POINTS
ON AN AERIAL LIFT. IT IS HERE THAT THE STRESSES OF LIFT-
ING ARE CONCENTRATED, AT THE CENTER OF ROTATION.
BECAUSE OF THIS, PROPER MAINTENANCE OF THE SWING
BEARING BOLTS IS A MUST FOR SAFE OPERATION.
Replacement
1. Removal.
a. From ground control station, operate the boom
lift control and raise boom adequately to provide
access to frame opening or, if equipped, to the
rotary coupling.
NEVER WORK BENEATH THE BOOM WITHOUT FIRST PROVIDING
ADEQUATE OVERHEAD SLING SUPPORT AND/OR BLOCKING.
b. Attach an adequate support sling to the boom
and draw all slack from sling. Block the boom if
feasible.
c. From under side of machine frame, remove bolts
and lockwashers which attach rotary coupling
retaining yoke to coupling housing.
HYDRAULIC LINES AND PORTS SHOULD BE CAPPED IMMEDI-
ATELY AFTER DISCONNECTING LINES TO AVOID THE ENTRY OF
CONTAMINANTS INTO THE SYSTEM.
Figure 2-16. Swing Bearing Tolerance Boom Placement